1. Field of the Invention
The present invention relates to an optical information recording medium such as DVD−RW (Digital Versatile Disc ReWritable), a method of generating a flag to be recorded onto the information recording medium, a method of producing the information recoding medium, a method of adjusting recording conditions of the information recording medium, a method of recording for the information recording medium, and an information recording device and particularly relates to an information recording medium capable of selecting a recording speed, the method of producing the same, a flag generating method, a method of adjusting recording conditions of the information recording medium, a method of recoding for the information recording medium, and the information recording device.
2. Description of the Related Art
Recently, recordable type optical discs such as a DVD-R, a DVD−RW, and a DVD+RW have been developed. Some optical discs among them are sold in a market together with information recording devices (drives) which record and reproduce information on the optical disc. When the information recording devices record information onto the optical disc, the devices confirm whether or not a power of a laser light for carrying out recording (hereinafter, referred to as a recording power) has a proper value. This confirmation operation is generally called OPC (Optimum Power Control), which is very important operation for the recordable type disc.
The optical information recording device has an optical head. The optical head emits a laser light, which is irradiated onto a recording surface of the optical disc. At the time, a recording power of the laser light to be irradiated onto the optical disc is changed corresponding to various factors. Therefore, the optical information recording device may allow the optical head to emit a laser light having a predetermined power, but in fact, the practical power of the laser light to be irradiated onto the optical disc is often shifted off from a proper range of the power. Then, a function of the OPC is that the recording power is calibrated based on an information obtained from a practical recorded signal.
For example, as described in the DVD−RW standard statement “DVD Specifications for Re-recordable Disc (DVD−RW) Part 1 PHYSICAL SPECIFICATIONS Version 1.1” and the DVD-R standard statement “DVD Specifications for Recordable Disc for General (DVD-R for General) Part 1 PHYSICAL SPECIFICATIONS Version 2.0”, as a method of OPC, a β method of using a β value having correlation with respect to an asymmetry value and a γ method of using a γ value having correlation with respect to a signal amplification (modulation) of a reproduced signal.
First, the β method will be explained as follows. FIG. 1 is a graph in which X-axis is defined by time and Y-axis is defined by output of signal, and by which the definition of the asymmetry value is explained. FIG. 2 is a graph in which X-axis is defined by time and Y-axis is defined by output of signal from which DC (direct current) component is removed, and by which the definition of the β value is explained. FIG. 3 is a graph in which X-axis is defined by a recording power and Y-axis is defined by an asymmetry value and a jitter value, and by which correlation among the recording power, the asymmetry value, and the jitter are shown.
After a relatively long period signal such as 11T single signal is recorded onto an optical disc, in which a longer mark (amorphous area) having a length which is eleventh times (11T) longer than a channel clock period T and a longer space (crystallized area) having a length of 11T are alternatively repeated, a relatively short period signal such as 3T single signal is recorded, which includes a shorter mark having 3T length and a shorter space having a 3T length, and these signals are reproduced. As a result, the output waveform is measured as shown in FIG. 1. A value of the output signal corresponding to the above-mentioned longer space is defined by V1, a value of the output signal corresponding to the above-mentioned longer mark is defined by V2, a value of the output signal corresponding to the above-mentioned shorter space is defined by V3, a value of the output signal corresponding to the above-mentioned shorter mark is defined by V4. Then, the value of V1 becomes greater than the value of V3, and the value of V2 becomes less than the value of V4. That is why the longer space becomes lighter than the shorter space and the longer mark becomes darker than the shorter mark, when a reproducing laser light is irradiated thereon. And, an asymmetry value A is defined by following equation 1. As shown by the equation 1, the asymmetrical value A is a value obtained by normalizing difference between the center of amplitude of the long period signal (11T single signal) and the center of amplitude of the short period signal (3T single signal).A={(V1+V2)−(V3+V4)}/{2×(V1−V2)}  [Equation 1]
Further, the β value is an asymmetry value to be easily calculated based on a signal obtained by removing the DC (direct current) component from the above-mentioned output signal. Its content is as same as that of the asymmetrical value to be defined by the equation 1. The β value can be obtained according to following procedures. Namely, in the optical information recording device (drive), a DC component is removed from the output signal shown in FIG. 1 to generate an AC signal. The output waveform is shown in FIG. 2. Then, if a value of the output signal corresponding to a longer space at the AC signal is defined by V5, a value of the output signal corresponding to a longer mark is defined by V6, the β value is defined by following equation 2.β=(V5+V6)/{2×(V5−V6)}  [Equation 2]
Here, an average value of the output signals shown in FIG. 1 is adopted as 0 level of the AC signal shown in FIG. 2. A practical output signal includes many short-period-components, so that the 0 level of the AC signal becomes substantially equal to the center of the amplitude of the short period signal. Accordingly, as represented by the equation 2, only output signal values V5 and V6 of signals, each whose period is long, are used in order to calculate the β value. However, information of the short period signal is included in the value of 0 level, so that the β value can be used as an asymmetry value. And, in a practical optical information recording device, a signal from which a DC component is removed, is often handled in order to ease amplification of signal using an amplifier. It takes more time to complete the calculation of the equation 1 than the calculation of the equation 2. Therefore, in the optical information recording device, the β value is often used as the asymmetry value.
And, as shown in FIG. 3, the asymmetry value (the β value) is dependent on a recording power. The higher the recording power is, the greater the asymmetry value becomes. Hereinafter, this reason will be explained. The greater the recording power is, the bigger a mark (amorphous portion) to be formed on the optical disc becomes. This mark becomes dark, so that corresponding output signal is lowered. The lowering of the output signal becomes more outstanding, as the mark becomes shorter. Accordingly, the output signal having a shorter mark is largely lowered in accompanying with the increase of the recording power. On the other hand, the output signal of the longer mark is not lowered so much. Thus, the more the recording power increases, the bigger difference between the output signal of the relatively shorter mark and the output signal of the relatively longer mark becomes, so that the asymmetry value will be increased.
In this way, the β method is a method of adjusting the recording power, using the characteristic that the asymmetry value has a recording power dependency. Namely, as shown in FIG. 3, the jitter value is dependent on the recording power, and there exists a recording power whose jitter value becomes minimum, i.e. an optimum laser power P1. However, the jitter value is a static amount, so that it is difficult to measure the value for a short time. Therefore, an asymmetry value A1 at a recording power P1 whose jitter value becomes minimum is beforehand measured, and the value A1 is set as an asymmetry value of a target. And, on the occasion of recording, by searching the recording power so as to obtain an asymmetry value A1 of the target, the recording power is adjusted. In this way, in order to perform OPC using the asymmetry value (the β value) by the β method, in view of its principle, it is necessary that the asymmetry value has a recording power dependency to some extent.
Next, the γ method will be briefly explained. The γ method is a method in which a signal amplitude of a reproduced signal is differentiated by a recording power, the γ value is obtained which is normalized by the magnitude of the signal amplitude, and the recording power that the γ value which becomes 1.5 is thereafter multiplied by 1.22, so that an optimum power is obtained.
Generally, the β method in which relation between the longer mark and the shorter mark is monitored, is more reliable than the γ method in which only signal amplitude is monitored. Further, in the γ method, the above-mentioned coefficients 1.5 and 1.22 are mere recommended values. Depending on an optical head and a medium, any other values may be desirable. Therefore, generally, the γ method is hard to use, i.e. this method is not used so actively.
However, in the above conventional arts, there is a following problem. Recently, a DVD−RW and a DVD+RW in which a phase change recording layer is used, have been able to be applied to high-speed recording. A medium whose range of applicable recording speed (cover range) is widely adopted, i.e. a medium which can record information not only at a specific speed but also at a speed which is higher than the specific speed is realized. Specifically, a medium is realized in which both recording at such a specific speed (1×-speed Write Strategy) and recording at a speed being twice as rapid as the specific speed (2×-speed Write Strategy) can be carried out.
However, the present inventors have found out that if recording is carried out at a relatively low speed with respect to the medium corresponding to high-speed recording in case of the phase change recording layer, an asymmetry value will not be dependent on the recording power. This reason is assumed as follows. It is necessary that a recorded information can be erased by irradiation of laser light for a shorter time than on the occasion of low-speed recording in order to enable high-speed recording by a phase change type medium. Therefore, the phase change recording layer needs to be easy to be crystallized. However, as a result, if recording is carried out by irradiating a laser light onto the phase change recording layer with a relatively greater recording power for a relatively long time on the occasion of low-speed recording, the mark which has been at once amorphous will be re-crystallized by remaining heat from the periphery of the heat, so that the mark will become less. Therefore, even if the recording power is increased, the mark will not become so large, so that the recording power dependency of a signal level corresponding to the mark becomes small. As a result, the recording power dependency of the asymmetrical value will become small.
Thus, the recording power dependency of the asymmetry value becomes small on the occasion of the low-speed recording, whereby the β method can be used on the occasion of high-speed recording, but the β method is not available on the occasion of low-speed recording using the same medium. For example, this causes following problems. If a recording power adjusting device employing the β method as OPC is mounted to a drive only corresponding to 1×-speed recording and thereafter this drive is on sale, there is no problem when a medium only corresponding to 1×-speed recording is used by the drive. However, thereafter, for example, in a case where a medium corresponding to both 1×-speed recording and 2×-speed recording appears, if such a novel medium is used by the above-mentioned drive only corresponding to 1×-speed recording, the drive can perform recording at only 1×-speed, so that the β method which cannot be used at 1×-speed recording is available for OPC to perform 1×-speed recording. This means that the drive erroneously learns the optimum recording power, resulting in that a normal recording will not be possible. Needless to say, such a situation should be avoided absolutely.